This invention relates generally to optical measuring apparatus and more particularly to a method and apparatus for determining the accurate alignment of an intense optical beam, typically but not restricted to a laser beam. One method for determining alignment of a laser beam for example, is taught in U.S. Pat. No. 3,915,574, whereupon a laser beam of coherent light having a plurality of components of different frequencies is projected along a path of alignment through an ambient medium having a varied index of refraction, detecting the components and then measuring the separation of the beam components.